Monochromatic light source

ABSTRACT

Light emitting systems are disclosed. The light emitting system includes an electroluminescent device that emits light at a first wavelength. The light emitting system further includes an optical cavity that enhances emission of light from a top surface of the light emitting system and suppresses emission of light from one or more sides of the light emitting system. The optical cavity includes a semiconductor multilayer stack that receives the emitted first wavelength light and converts at least a portion of the received light to light of a second wavelength. The semiconductor multilayer stack includes a II-VI potential well. The integrated emission intensity of all light at the second wavelength that exit the light emitting system is at least 10 times the integrated emission intensity of all light at the first wavelength that exit the light emitting system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage filing under 35 U.S.C. 371 ofPCT/US2009/051920, filed on Jul. 28, 2009, which claims priority to U.S.Provisional Application No. 61/094,267 filed on Sep. 4, 2008, thedisclosure of which is incorporated by reference in its/their entiretyherein.

FIELD OF THE INVENTION

This invention generally relates to semiconductor light sources. Theinvention is particularly applicable to semiconductor light sources thatinclude one or more II-VI semiconductor compounds.

BACKGROUND

Laser diodes are used in many different applications such as laserpointers, projection displays, and sensors. Laser diodes that emit inthe near UV, violet, near infrared, or infrared regions of the spectrumcan be compact and inexpensive. In other regions of the spectrum,however, known laser diodes, such as frequency doubled laser diodes, arecomplicated, bulky, inefficient, and expensive. There is a great needfor a compact, efficient, and inexpensive laser diode system capable ofemitting at other desirable wavelengths, such as in the cyan, green,charteuse, yellow and amber regions of the spectrum.

SUMMARY OF THE INVENTION

Generally, the present invention relates to semiconductor light sources.In one embodiment, a light source includes a III-V based pump lightsource that includes nitrogen and emits light at a first wavelength. Thelight source further includes a vertical cavity surface emitting laser(VCSEL) that converts at least a portion of the first wavelength lightemitted by the pump light source to at least a partially coherent lightat a second wavelength. The VCSEL includes first and second mirrors thatform an optical cavity for light at the second wavelength. The firstmirror is substantially reflective at the second wavelength and includesa first multilayer stack. The second mirror is substantiallytransmissive at the first wavelength and partially reflective andpartially transmissive at the second wavelength. The second mirrorincludes a second multilayer stack. The VCSEL further includes asemiconductor multilayer stack that is disposed between the first andsecond mirrors and converts at least a portion of the first wavelengthlight to the second wavelength light. The semiconductor multilayer stackincludes a quantum well that includes a Cd(Mg)ZnSe alloy.

In another embodiment, a light source includes a III-V based pump lightsource that includes nitrogen N and emits light at a first wavelength.The light source further includes an optical assembly that converts atleast a portion of the first wavelength light emitted by the pump lightsource to at least a partially coherent light at a second wavelength.The optical assembly includes first and second mirrors that form anoptical cavity for light at the second wavelength. The first mirror issubstantially reflective at the second wavelength and includes a firstmultilayer stack. The second mirror is partially reflective at thesecond wavelength. The optical assembly further includes a semiconductormultilayer stack that is disposed between the first and second mirrorsand converts at least a portion of the first wavelength light to thesecond wavelength light. The semiconductor multilayer stack includes aquantum well that includes a Cd(Mg)ZnSe alloy.

In another embodiment, a light emitting system includes anelectroluminescent device that emits light at a first wavelength. Thelight emitting system further includes an optical cavity that enhancesemission of light from a top surface of the light emitting system andsuppresses emission of light from one or more sides of the lightemitting system. The optical cavity includes a semiconductor multilayerstack that receives the emitted first wavelength light and converts atleast a portion of the received light to light of a second wavelength.The semiconductor multilayer stack includes a II-VI potential well. Theintegrated emission intensity of all light at the second wavelength thatexit the light emitting system is at least 10 times the integratedemission intensity of all light at the first wavelength that exit thelight emitting system. In some cases, the II-VI potential well includesCd(Mg)ZnSe or ZnSeTe. In some cases, the electroluminescent device is sodesigned that a substantial portion of the first wavelength light thatis received by the semiconductor multilayer stack, exits theelectroluminescent device through a top surface of theelectroluminescent device. In some cases, light that is emitted by thelight emitting system along a first direction has a first set of colorcoordinates and light that is emitted by the light emitting system alonga second direction different than the first direction has a second setof color coordinates, where the second set of color coordinates issubstantially the same as the first set of color coordinates. In somecases, the first set of color coordinates are u₁′ and v₁′ and the secondset of color coordinates are u₂′ and v₂′, and the absolute value of eachof differences between u₁′ and u₂′ and between v₁′ and v₂′ is no morethan 0.003. In some cases, a primary portion of the re-emitted secondwavelength light exits the light emitting system from a top surface ofthe light emitting system. The top surface has a minimum lateraldimension W_(min). A substantial fraction of the remaining portion ofthe re-emitted second wavelength light exits the light emitting systemfrom one or more sides of the optical cavity that have a maximum edgethickness T_(max). The ratio W_(min)/T_(max) is at least about 30. Aprimary portion of the emitted first wavelength light exits theelectroluminescent device from a top surface of the electroluminescentdevice. The top surface has a minimum lateral dimension W1 _(min). Theremaining portion of the emitted first wavelength light exits theelectroluminescent device from one or more sides of theelectroluminescent device that have a maximum edge thickness T1 _(max).The ratio W1 _(min)/T1 _(max) is at least about 30. In some cases, eachof the ratios W_(min)/T_(max) and W1 _(min)/T1 _(max) is at least about100.

BRIEF DESCRIPTION OF DRAWINGS

The invention may be more completely understood and appreciated inconsideration of the following detailed description of variousembodiments of the invention in connection with the accompanyingdrawings, in which:

FIG. 1 is a schematic side-view of a light source;

FIG. 2 is a schematic side-view of a light source that includes an arrayof discrete light sources;

FIG. 3A-3E are schematic representations of devices at intermediatestages or steps in a process for fabricating a light source;

FIG. 4 is a schematic side-view of another light source;

FIG. 5 is a schematic side-view of another light source;

FIG. 6 is a schematic side-view of a light emitting system; and

FIG. 7 is a schematic view of a light pointer.

The same reference numeral used in multiple figures refers to the sameor similar elements having the same or similar properties andfunctionalities.

DETAILED DESCRIPTION

This application discloses semiconductor light sources that include oneor more pump light sources and one or more semiconductor opticalcavities for converting light emitted by a pump light source to adifferent wavelength light. In some cases, a disclosed semiconductoroptical cavity is a resonant-cavity capable of converting, such as downconverting, an incident light. In some cases, a disclosed semiconductorresonant-cavity wavelength converter is a vertical cavity surfaceemitting laser (VCSEL). The disclosed light sources are efficient,compact, and in some cases, inexpensively integrate a light convertingVCSEL with a pump light source from two or more different semiconductorgroups. For example, this application discloses a light source thatintegrates a III-V pump light source, such as a pump light source thatincludes N, such as a AlGaInN pump LED or a laser diode, with a II-VIVCSEL that includes a II-VI semiconductor wavelength converter, such asa Cd(Mg)ZnSe wavelength converter.

In some cases, the pump light source, such as a laser diode (LD) lightsource, is at least a partially coherent light source, meaning that itemits at least partially coherent light. In some cases, the pump lightsource, such as a light emitting diode (LED) light source, is anincoherent light source, meaning that it emits incoherent light.

In some cases, the semiconductor VCSEL and the pump light source arefrom the same semiconductor group, such as the III-V group. In suchcases, it may be feasible to monolithically grow and fabricate, forexample, a III-V VCSEL directly onto a III-V pump light source, such asa III-V pump. In some cases, however, a VCSEL that emits light at adesired wavelength and has high conversion efficiency and/or otherdesirable properties, is from a semiconductor group that is differentthan the group the pump LD or LED belongs to. For example, a VCSEL canbe from the II-VI group and a light source, such as an LD or LED, can befrom the III-V group. In such cases, it may not be possible or feasibleto grow one component onto the other with high quality. In such cases,the VCSEL can be attached to the pump light source to form a hybridlight source. Such hybrid light sources can emit light with high overallefficiency at different wavelengths in, for example, the visible regionof the spectrum. Exemplary methods of attaching two constructions aredescribed in U.S. Patent Application Ser. No. 60/978,304, filed Oct. 8,2007, which is incorporated herein in its entirety by reference.

In some cases, the disclosed light sources can output, for example, oneor more primary colors such as blue, green, or red in the RGB primarycolor system or cyan, magenta, and yellow in the CMYK primary colorsystem. In some cases, the disclosed light sources can output lighthaving other colors, such as amber or white. The emission efficiency andcompactness of the disclosed light sources can lead to new and improvedoptical systems, such as efficient projection systems, with reducedweight, size, and power consumption.

In some cases, the VCSEL can include a potential or quantum well, suchas a semiconductor potential or quantum well, that can convert light toa longer wavelength light. In some cases, the disclosed light sourcesefficiently integrate one or more VCSELs from a semiconductor group,such as the II-VI group, with one or more pump light sources, such aspump LDs or LEDs, from a different semiconductor group, such as theIII-V group.

An array of light sources is disclosed that include an array of pumplight sources and a corresponding array of VCSELs. Such an array oflight sources can form monochromatic (for example, green or green andblack) or color images. The disclosed arrays of light sources cancombine the primary functions of conventional light sources and imageforming devices resulting in reduced power consumption, size, and cost.For example, in a display system, a disclosed array of light sources canfunction as both the light source and the image forming device, therebyeliminating or reducing the need for a separate backlight or a spatiallight modulator. As another example, incorporating the disclosed arrayof light sources in a projection system eliminates or reduces the needfor image forming devices and relay optics.

Array of light sources is disclosed that can form, for example, an arrayof pixels in a display system. At least some of the light sourcesinclude a pump electroluminescent device, such as a pump LD or LED, thatis capable of emitting light in response to an electric signal. At leastsome of the light sources can include one or more VCSELs that includeone or more light converting elements, such as one or more potentialwells and/or quantum wells, for down converting light that is emitted bythe pump electroluminescent devices. As used herein, down convertingmeans that the photon energy of the converted light is less than thephoton energy of the pump light, or that the wavelength of the convertedlight is longer than the wavelength of the unconverted or incidentlight.

The disclosed arrays of light sources can be used in, for example,illumination systems, such as adaptive illumination systems, for use in,for example, projection systems or other optical systems.

FIG. 1 is a schematic side-view of a light source 100 that includes aIII-V based pump light source 170 that includes nitrogen, N, and emitslight 172 at a first wavelength λ₁. In some cases, light source 170 hasan emission spectrum with one or more peaks with wavelength λ₁ being thewavelength of a peak emission. In some cases, light source 170 emitslight essentially at a single wavelength λ₁, meaning that the emittedspectrum has a narrow peak at λ₁ and a small full spectral-width at halfmaximum (FWHM). In such cases, the FWHM can be less than about 50 nm, orless than about 10 nm, or less than about 5 nm, or less than about 1 nm.In some cases, the pump light source is a III-V laser diode. In somecases, the pump wavelength λ₁ is between about 350 nm and about 500 nm.For example, in such cases, λ₁ can be about 405 nm.

Light source 100 also includes a vertical cavity surface emitting laser(VCSEL) 190 that converts at least a portion of first wavelength light172 emitted by pump light source 170 to at least a partially coherentoutput light 178 at a second wavelength λ₂.

VCSEL 190 includes first mirror 120 and second mirror 160 that form anoptical cavity for light at the second wavelength. In some cases, theoptical thickness of the optical cavity can be an odd integer multipleof half of the second wavelength λ₂ (that is, (2m+1)(λ₂/2), where m isan integer). In such cases, a node of an optical standing wave at λ₂within the optical cavity is located at or close to the center of theoptical cavity. In some cases, the optical thickness of the opticalcavity can be an integer multiple of the second wavelength λ₂ (that is,mλ₂, where m is an integer). In such cases, an anti-node of an opticalstanding wave at λ₂ within the optical cavity is located at or close tothe center of the optical cavity.

In some cases, first mirror 120 is substantially reflective at thesecond wavelength. For example, in such cases, the reflectance of firstmirror 120 at the second wavelength λ₂ is at least 80%, or at least 90%,or at least 95%, or at least 99%, or at least 99.5%, or at least 99.9%.In some cases, first mirror 120 is substantially transmissive at thefirst wavelength λ₁. For example, in such cases, the opticaltransmittance of first mirror 120 at λ₁ is at least 50%, or at least60%, or at least 70%, or at least 80%, or at least 90%.

In some cases, such as in the exemplary light source 100 shown in FIG.1, first mirror 120 is or includes a first Bragg reflector 120. TheBragg reflector includes a multilayer stack of alternating low indexlayers 122 having a lower index of refraction and high index layers 124having a higher index of refraction. In the exemplary light source 100,first Bragg reflector 120 includes four low index layers 122 and fourhigh index layers 124. In general, first Bragg reflector 120 can includeone or more low index layers 122 and one or more high index layers 124.For example, in some cases, first Bragg reflector 120 can have at least5 low index layers and 5 high index layers, or at least 10 low indexlayers and 10 high index layers, or at least 15 low index layers and 15high index layers.

In some cases, the optical thickness of at least some of the low and/orhigh index layers in first Bragg reflector 120 is a quarter of thesecond wavelength in that layer. In such cases, for a quarter wave thicklayer, the physical thickness is λ₂/4n, where n is the index ofrefraction of the layer at λ₂.

First Bragg reflector 120 can include any materials that have suitablelower and higher indices of refraction. Exemplary materials includeSiO₂, Si₃N₄, TiO₂, Ta₂O₅, MgF₂, CaF₂, and HfO₂. In some cases, firstBragg reflector 120 can include a II-VI material such as ZnSe, ZnS,Cd(Mg)ZnSe, or Mg(Zn)Se, or any combinations or alloys thereof.

In some cases, second mirror 160 is partially reflective at the secondwavelength λ₂. In such cases, the reflectance of second mirror 160 atthe second wavelength λ₂ is at least 80%, or at least 90%, or at least95%, or at least 99%, or at least 99.5%, or at least 99.9%. In somecases, second mirror 160 is partially transmissive at the secondwavelength λ₂. In such cases, the optical transmittance of the secondmirror at the second wavelength is no more than 5%, or no more than 3%,or no more than 2%, or no more than 1%, or no more than 0.5%.

In some cases, such as in the exemplary light source shown in FIG. 1,second mirror 160 is or includes a second Bragg reflector that includesa multilayer stack of alternating low index layers 162 having a lowerindex of refraction and high index layers 164 having a higher index ofrefraction. In the exemplary light source 100, second Bragg reflector160 includes three low index layers 162 and three high index layers 164.In general, second Bragg reflector 160 can include one or more low indexlayers 162 and one or more high index layers 164. For example, in somecases, second Bragg reflector 160 can have at least 5 low index layersand 5 high index layers, or at least 10 low index layers and 10 highindex layers, or at least 15 low index layers and 15 high index layers.

In some cases, the optical thickness of at least some of the low and/orhigh index layers in second Bragg reflector 160 is a quarter of thesecond wavelength in that layer. In such cases, the physical thicknessis λ₂/4n, where n is the index of refraction of the layer at λ₂.

Light source 100 further includes a semiconductor multilayer stack 130that is disposed between first and second mirrors 120 and 160,respectively. Multilayer stack 130 converts at least a portion of firstwavelength light 174 to second wavelength light 176. In some cases, theconversion of light from the first wavelength to the second wavelengthcan be accomplished when semiconductor multilayer stack 130 absorbs atleast a portion of light 174 and re-emits at least a portion of theabsorbed light as light 176 at the second wavelength. In some cases,pump light source 170 can emit UV or violet light and the semiconductormultilayer stack 130 can re-emit blue, green, yellow, amber or redlight. In some cases, pump light source 170 can emit blue light and there-emitting semiconductor multilayer stack 130 can re-emit green,yellow, amber or red light.

Semiconductor multilayer stack 130 includes respective first and secondwindows 132 and 134; and a potential well stack that includes aplurality of alternating potential wells and light absorbing layers. Inparticular, the exemplary semiconductor multilayer stack 130 includesrespective first, second, and third absorbing layers 140, 142, and 144;and respective first and second potential wells 152 and 154.

The light absorbing layers in semiconductor multilayer stack 130 absorbat least a portion of first wavelength light 174 and, resultingresponse, produce photo-generated carriers, such as photo-generatedelectron-hole pairs. The carriers diffuse from the light absorbinglayers to the neighboring potential wells in the semiconductormultilayer stack, where they recombine radiatively and emit light at thesecond wavelength λ₂.

In some cases, such as when the density of the photo-generatedelectron-hole pairs in semiconductor multilayer stack 130 issufficiently high, second wavelength light 176 can be amplified as ittravels back and forth between mirrors 120 and 160. The amplificationoccurs primarily in the potential wells where the propagating lightassists in the recombination of carriers by means of stimulated emissionof light at the second wavelength λ₂. In such cases, if mirrors 120 and160 are sufficiently reflective at λ₂, the mirrors can effectivelyincrease the number of times light 176 passes through the potentialwells. As a result, the VCSEL can generate coherent or at leastpartially coherent light at λ₂.

In general, re-emitting multilayer stack 130 includes at least one layerof a II-VI compound that is capable of converting at least a portion ofa light, such as a blue or UV light, to a longer wavelength light. Insome cases, the II-VI wavelength converter includes a II-VI potential orquantum well.

As used herein, potential well means semiconductor layer(s) in amultilayer semiconductor structure designed to confine a carrier in onedimension only, where the semiconductor layer(s) has a lower conductionband energy than the surrounding layers and/or a higher valence bandenergy than the surrounding layers. Quantum well generally means apotential well which is sufficiently thin that quantization effectsincrease the energy for electron-hole pair recombination in the well. Aquantum well typically has a thickness of about 100 nm or less, or about10 nm or less.

In some cases, potential or quantum well 152 and/or 154 is a II-VIsemiconductor potential or quantum well that has a band gap energy thatis smaller than the energy of a photon emitted by pump light source 170.In general, the transition energy of potential or quantum well 152and/or 154 is substantially equal to the energy of a photon that isre-emitted by the potential or quantum well.

In some cases, potential wells 152 and 154 can include CdMgZnSe alloyshaving compounds ZnSe, CdSe, and MgSe as the three constituents of thealloy. In some cases, one or more of Cd, Mg, and Zn, especially Mg, maybe absent from the alloy. For example, potential wells 152 and 154 caninclude a Cd_(0.70)Zn_(0.30)Se quantum well capable of re-emitting inthe red, or a Cd_(0.33)Zn_(0.67)Se quantum well capable of re-emittingin the green. As another example, potential wells 152 and 154 caninclude an alloy of Cd, Zn, Se, and optionally Mg, in which case, thealloy system can be represented by Cd(Mg)ZnSe. As another example,potential wells 152 and 154 can include an alloy of Cd, Mg, Se, andoptionally Zn. In some cases, the potential wells can include ZnSeTe. Insome cases, a quantum well 152 or 154 has a thickness in a range fromabout 1 nm to about 100 nm, or from about 2 nm to about 35 nm. In somecases, potential wells 152 and 154 can include Be, Hg, O, S or Te, or analloy of the same.

In some cases, potential wells 152 and 154 are capable of converting atleast a portion of light that is emitted by pump light source 170 to alonger wavelength light. In some cases, potential wells 152 and 154 caninclude a II-VI potential well. In general, potential wells 152 and 154can have any conduction and/or valence band profile. Exemplary profilesare described in, for example, U.S. Patent Application No. 60/893,804which is incorporated herein by reference in its entirety.

The separation between neighboring potential wells, such as potentialwells 152 and 154, can be any distance that may be practical and/ordesirable in an application. For example, in some cases, the first andsecond potential or quantum wells can be separated by a distance that isabout half of the second wavelength λ₂ in the medium that separates thetwo potential wells. For example, in such cases, the separation betweenpotential wells 152 and 154 can be λ₂/2n, where n is the index ofrefraction of layer 142 at the second wavelength λ₂.

In some cases, at least a portion of semiconductor multilayer stack 130is doped with a dopant. For example, in some cases, potential wells 152and 154 can be n-doped or p-doped where the doping can be accomplishedby any suitable method and by inclusion of any suitable dopant, such asCl, Br, I, Al, Ga, or N.

In some cases, pump light source 170 and semiconductor multilayer stack130 can be from two different semiconductor groups. For example, in somecases, pump light source 170 can be a III-V semiconductor device andsemiconductor multilayer stack 130 can be a II-VI semiconductor device.In some cases, pump light source 170 can include AlGaInN semiconductoralloys and semiconductor multilayer stack 130 can include Cd(Mg)ZnSesemiconductor alloys.

The exemplary semiconductor multilayer stack 130 in FIG. 1 includes twopotential wells 152 and 154. In general, semiconductor multilayer stack130 can have one or more potential or quantum wells. In some cases,semiconductor multilayer stack 130 can have a single potential orquantum well. In some cases, semiconductor multilayer stack 130 can have2 or more potential wells, or 5 or more potential wells, or 10 or morepotential wells. In some cases, at least some or all of the potentialwells in the multilayer stack 130 can be located at or near theantinodes of the optical cavity modes at the second or emissionwavelength λ₂.

Light absorbing layers 140, 142 and 144 assist in absorption of light174 and generation of carriers. The light absorbing layers are placedproximate the potential wells in semiconductor multilayer stack 130 sothat the photo-generated carriers can efficiently diffuse to thepotential wells for radiative recombination of carriers and emission oflight at the second wavelength λ₂.

In some cases, a light absorbing layer in semiconductor multilayer stack130 can be immediately adjacent to one or more corresponding potentialwells, meaning that no intervening layer is disposed between theabsorbing layer and the potential well. For example, first lightabsorbing layer 140 is immediately adjacent corresponding firstpotential well 152. As another example, second light absorbing layer 142is immediately adjacent corresponding potential wells 152 and 154. Insome cases, a light absorbing layer in semiconductor multilayer stack130 can be closely adjacent to a corresponding potential well, meaningthat one or a few intervening layers may be disposed between theabsorbing layer and the potential well. For example, in some cases, oneor more intervening layers can be disposed between first light absorbinglayer 140 and corresponding first potential well 152. In such cases, theintervening layers do not substantially block, or interfere with, thediffusion of carriers from absorbing layer 140 to potential well 152.For example, the intervening layers can be sufficiently thin and/or havesufficiently low band gap energies to allow diffusion of carriers fromthe absorbing layer to the potential well.

In some cases, a light absorbing layer can include a semiconductor, suchas an inorganic semiconductor, such as a II-VI semiconductor. Forexample, one or more of absorbing layers 140, 142 and 144 can include aCd(Mg)ZnSe semiconductor alloy. In some cases, one or more of absorbinglayers 140, 142 and 144 can include Be, Hg, O, S or Te, or an alloythereof.

In some cases, a light absorbing layer can have a band gap energy thatis smaller than the energy of a photon emitted by pump light source 170.In such cases, the light absorbing layer can strongly absorb light thatis emitted by the pump light source. In some cases, a light absorbinglayer can have a band gap energy that is greater than the transitionenergy of potential well 140. In such cases, the light absorbing layeris substantially optically transparent to light that is re-emitted bythe potential well.

In some cases, at least one light absorbing layer in semiconductormultilayer stack 130 is doped with a dopant. In some cases, the dopantcan include chlorine or iodine. In some cases, a light absorbing layercan be n-doped or p-doped where the doping can be accomplished by anysuitable method and by inclusion of any suitable dopant. In some cases,the number density of the dopant is in a range from about 10¹⁷ cm⁻³ toabout 10¹⁸ cm⁻³. Other exemplary dopants include Al, Ga, In, F, Br, andN.

The exemplary semiconductor multilayer stack 130 includes three lightabsorbing layers 140, 142 and 144. In general, the semiconductormultilayer stack can have no, one, two, or more than two light absorbinglayers. In general, a light absorbing layer is sufficiently close to oneor more corresponding potential wells so that a photo-generated carrierin the light absorbing layer has a reasonable chance of diffusing to thepotential well. In cases where the semiconductor multilayer stack doesnot include light absorbing layers, the potential wells can besubstantially light absorbing at the first wavelength λ₁.

First and second windows 132 and 134 are designed primarily to providebarriers so that carriers, such as electron-hole pairs, that arephoto-generated in an absorbing layer do not, or have a small chance to,migrate to a free or external surface of, for example, semiconductormultilayer stack 130 where they can recombine non-radiatively. In somecases, windows 132 and 134 have band gap energies that are greater thanthe energy of a photon emitted by pump light source 170. In such cases,windows 132 and 134 are substantially optically transparent to lightemitted by pump light source 170 at the first wavelength λ₁ and to lightthat is re-emitted by, for example, first potential well 140 at thesecond wavelength λ₂.

Exemplary light source 100 includes two windows. In general, a lightsource can have no or any number of windows. For example, in some cases,light source 100 can have a single window disposed between pump lightsource 170 and first potential well 152, or between pump light source170 and first light absorbing layer 140. In some cases, such as in theexemplary semiconductor multilayer stack 130, at lease one window, suchas windows 132 and 134, is an outermost layer of the semiconductormultilayer stack.

In some cases, the location of an interface between two adjacent layersin light source 100 may be a well-defined or sharp interface. In somecases, such as when the material composition within a layer changes as afunction of distance along the thickness direction, the interfacebetween two adjacent layers may not be well defined and may, forexample, be a graded interface. For example, in some cases, first lightabsorbing layer 140 and first window 132 can have the same materialcomponents but with different material concentrations. In such cases,the material composition of the light absorbing layer may be graduallychanged to the material composition of the window layer resulting in agraded interface between the two layers. For example, in cases whereboth layers include Mg, the concentration of Mg can be increased whengradually transitioning from the absorbing layer to the window.

In some cases, a portion of emitted light 174 can be transmitted bysemiconductor multilayer stack 130 as light 174A at the first wavelengthλ₁ which may, in turn, be transmitted, at least partially, by secondmirror 160 as light 174B at the first wavelength. In such cases, outputlight 178 of light source 100 can include light at the first and secondwavelengths. For example, in such cases, emitted light 174 can be blueand re-emitted light 176 can be yellow, resulting in a white outputlight 178.

Light source 100 further includes optional light management optics 180for managing light 172 emitted by pump light source 170. For example,light management optics 180 can include one or more optical lenses forfocusing light 172. Other exemplary light management optics includeoptical filters, polarizers, beam splitters, dichroic mirrors, andoptical fibers.

In the exemplary light source 100, VCSEL 190 is disposed on a heat sink105. The heat sink cools VCSEL 190 by transferring or conducting heatthat is generated in the VCSEL to a different location such as theenvironment. In some cases, heat sink 105 can be a water-cooling heatsink. In some cases, heat sink 105 can be substantially opticallytransmissive at the first wavelength λ₁. For example, in such cases, theoptical transmission of heat sink 105 at the first wavelength λ₁ is atleast 50%, or at least 60%, or at least 70%, or at least 80%, or atleast 90%.

In general, heat sink 105 can include any material suitable forconducting heat away from VCSEL 190. Exemplary heat sink materialsinclude silicon. Exemplary transparent heat sink materials includesilicon carbide, sapphire, and diamond. In some cases, the heat sink caninclude an opaque material, such as a metal. In such cases, the heatsink can include one or more small transparent or clear openings toallow pump light 174 to pass through.

In general, pump light source 170 can be any light source capable ofemitting light at a desired wavelength or in a desired wavelength range.For example, in some cases, pump light source 170 can be an LED emittingincoherent UV, violet or blue light. In some cases, pump light source170 can be a III-V semiconductor light source, such as a III-V LED, andmay include AlGaInN semiconductor alloys. For example, pump light source170 can be a GaN based LED.

In some cases, pump light source 170 can include one or more p-typeand/or n-type semiconductor layers, one or more active layers that mayinclude one or more potential and/or quantum wells, waveguide layers,cladding layers, buffer layers, substrate layers, and superstratelayers.

In some cases, pump light source 170 can be attached or bonded to heatsink 105 or, if, for example, heat sink 105 is absent or is locatedelsewhere, to first mirror 120. The attachment or bonding can beachieved by any suitable method such as by an adhesive such as a hotmelt adhesive, welding, pressure, heat or any combinations of suchmethods or other methods that may be desirable in an application.Examples of suitable hot melt adhesives include semicrystallinepolyolefins, thermoplastic polyesters, and acrylic resins.

Other exemplary bonding materials include optically clear polymericmaterials, such as optically clear polymeric adhesives, includingacrylate-based optical adhesives, such as Norland 83H (supplied byNorland Products, Cranbury N.J.); cyanoacrylates such as Scotch-Weldinstant adhesive (supplied by 3M Company, St. Paul, Minn.);benzocyclobutenes such as Cyclotene™ (supplied by Dow Chemical Company,Midland, Mich.); clear waxes such as CrystalBond (Ted Pella Inc.,Redding Calif.); liquid, water, or soluble glasses based on sodiumsilicate; and spin-on glasses (SOG).

In some cases, pump light source 170 can be attached or bonded to heatsink 105 or to first mirror 120 by, for example, disposing one or morebonding layers between the two during the bonding process. A bondinglayer can, for example, include one or more thin or very thin metallayers, one or more thin metal oxide layers, or one or more layers ofother materials such as adhesives, encapsulants, high index glasses, orsol-gel materials such as low temperature sol-gel materials, or anycombinations thereof.

In general, pump light source 170 can be an incoherent, partiallycoherent, or coherent light source. For example, in some cases, pumplight source 170 can be a coherent pump light source, such as a pumplaser such as a pump laser diode, emitting coherent light 172. In somecases, pump light source 170 can be an incoherent pump light source,such as a pump light emitting diode (LED) emitting incoherent light 172.In some cases, such as when mirrors 120 and 160 are highly reflective atλ₂ and potential wells 152 and 154 provide sufficient gain at λ₂, lightsource 100 can be a laser or a coherent light source emitting coherentoutput light 178. In some cases, output light 178 can be incoherent orpartially coherent.

In some cases, pump light source 170 can emit light 172 that includes ordisplays an image. For example, pump light source 170 can include a oneor two dimensional array of discrete light sources that can beindividually modulated to form an image. For example, FIG. 2 shows aschematic side-view of a light source 200 that includes an array ofdiscrete light sources 200-1, where at least one discrete light sourceincludes a discrete pump light source and a discrete VCSEL. Inparticular, the exemplary light source 200 includes an array of discretepump light sources 270 emitting a corresponding array of emitted lights272, and a corresponding array of discrete VCSELs 290 re-emitting acorresponding array of re-emitted lights 276. In the exemplary lightsource 200, array 270 includes discrete pump light sources 270-1 through270-5 emitting respective pump lights 272-1 through 272-5, and array 290includes VCSEL 290-1 through 290-5 re-emitting respective lights 276-1through 276-5. For example, VCSEL 290-1 absorbs at least a portion ofemitted pump light 272-1 and re-emits at least a portion of the absorbedlight as light 276-1 at a longer wavelength.

In some cases, at least some of the discrete pump light sources emitlight in different color regions of the spectrum. For example, emittedpump light 272-1 can be a UV light and emitted pump light 272-3 can be ablue light. In some cases, all the discrete pump light sources can emitlight in the same color region of the spectrum. For example, all thediscrete pump light sources can emit blue light. In some cases, thewavelengths of the pump lights that are emitted in the same color regionare substantially equal. For example, in such cases, the differencebetween the emitted wavelengths is no more than about 50 nm, or about 40nm, or about 30 nm, or about 20 nm, or about 10 nm, or about 7 nm, orabout 5 nm.

In some cases, at least some of the re-emitted lights 276-1 through276-5 can have different wavelengths. For example, re-emitted light276-1 can be a blue light, re-emitted light 276-3 can be a green light,and re-emitted light 276-5 can be a red light.

In some cases, light source 200 can include a discrete pump light sourcewithout a corresponding VCSEL. For example, Light source 200 can includediscrete pump light source 270-1, but VCSEL 290-1 may be absent in thelight source. In such cases, the light emitted by pump light source270-1 can be part of the overall light emitted by light source 200. Asanother example, pump light source 270-1 can emit blue light and nothave a corresponding VCSEL, pump light source 270-2 can emit blue lightwith corresponding VCSEL 290-2 re-emitting green light, and pump lightsource 270-3 can emit blue light with corresponding VCSEL 290-3re-emitting red light. In such cases, emitted blue light 272-1,re-emitted green light 276-2, and re-emitted red light 276-3 can combineto produce white light. In such cases, pump light sources 270-1, 270-2and 270-3 can be part of a same pixel in light source 200 with eachindividual pump light source being part of a sub-pixel.

Referring back to FIG. 1, light source 100 can be included in a display.For example, a pixel in a pixelated display that is capable ofdisplaying a pixelated image, can include light source 100. In somecases, each pixel in a pixelated display can include a light sourcesimilar to light source 100, where in some pixels, the semiconductormultilayer stack may be absent.

In some cases, the discrete pump light sources in array 270 can bemodulated independently to form an emitted image, for example, in blue.The discrete VCSELs in array of VCSELs 290 can convert the emitted imageinto a re-emitted pixelated image at a surface, such as surface 295, oflight source 200. In some cases, the re-emitted pixelated image can be amonochromatic (for example, green or green and black) image. In somecases, the re-emitted pixelated image can be a color image. In thecontext of a display system, a discrete light source in light source 200can be, for example, a pixel or a sub-pixel.

In general, the array of discrete light sources in light source 200 canbe any type array desirable in an application. In some cases, the arraycan be a row or a column, such as a 1×n array where n is 2 or greater.In some cases, the array can be a square array, such as an m×m array, ora rectangular array, such as an m×n array where n and m are both 2 orgreater and m is different than n. In some cases, the array can be atrapezoidal array, a hexagonal array, or any other type array, such asany regular or irregular type array.

In some cases, the discrete light sources in the array (or pixels in thearray in the context of a display system) can be of equal size, or havedifferent sizes, for example, to account for differences in conversionefficiency of different colors.

A discrete light source in an array of discrete light sources can haveany shape such as, square, oval, rectangular, or more complex shapes toaccommodate, for example, optical and electrical functions of a deviceincorporating the array. The discrete light sources in an array can beplaced in any arrangement that may be desirable in an application. Forexample, the elements can be uniformly spaced, for example, in arectangular or hexagonal arrangement. In some cases, the elements can beplaced non-uniformly, for example, to improve device performance by, forexample, reducing or correcting optical aberrations such as pincushionor barrel distortions.

Light sources disclosed in this application can be fabricated usingmethods commonly used in, for example, fabrication of microelectronicand semiconductor devices and other wafer-based devices. Known methodsinclude molecular-beam epitaxy (MBE), metal-organic vapor-phase epitaxy(MOVPE), physical vapor deposition (PVD), chemical vapor deposition(CVD), metal-organic vapor phase deposition (MOCVD), liquid phaseepitaxy (LPE), vapor phase epitaxy (VPE), photolithography, waferbonding, deposition methods and etching methods. An exemplary processfor fabricating a light source similar to light source 100 isschematically outlined in reference to FIGS. 3A-3E.

First, semiconductor multilayer stack 130 is fabricated on a substrate310 as shown schematically in FIG. 3A where the details of stack 130,some of which are shown in FIG. 1, are not shown in FIG. 3A for ease ofviewing. Substrate 310 can be any substrate that may be suitable and/ordesirable in an application. For example, substrate 310 can be asapphire substrate, a SiC substrate, a GaN substrate, or an InPsubstrate.

In some cases, semiconductor multilayer stack 130 is grownpseudomorphically on InP, meaning that the lattice constant of at leastone layer in stack 130, such as a layer that is immediately adjacentsubstrate 310, is sufficiently similar to the lattice constant of acrystalline substrate 310 so that when fabricating or growing thesemiconductor multilayer stack on the substrate, the multilayer stackcan adopt the lattice spacing of the substrate with no or low density ofmisfit defects. In such cases, the lattice constant of at least some ofthe layers in semiconductor multilayer stack 130 can be constrained tothe lattice constant of the substrate.

In some cases, semiconductor multilayer stack 130 is or includes a layerthat is lattice matched to substrate 310, meaning that the latticeconstant of a crystalline semiconductor multilayer stack 130 issubstantially equal to the lattice constant of a crystalline substrate310 where by substantially equal it is meant that the two latticeconstants are not more than about 0.2%, or not more than about 0.1%, ornot more than about 0.01%, different from each other. In some cases,such as when substrate 310 includes InP, semiconductor multilayer stack130 can be lattice matched to InP.

Next, first mirror 120 is fabricated on semiconductor multilayer stack130 as shown schematically in FIG. 3B, where the details of first mirror120, some of which are shown in FIG. 1, are not shown in FIG. 3B forease of viewing. The different layers in first mirror 120 can befabricated on semiconductor multilayer stack 130 using, for example,chemical and/or physical vapor deposition methods. In some cases, ahighly reflecting metal layer can be included in first mirror 120.

Next, heat sink 105 is attached to first mirror 120 as shownschematically in FIG. 3C. Heat sink 105 includes a material with a highthermal conductivity such as a metal. The attachment may be made usingany suitable method, such as solder bonding, direct wafer bonding, oradhesive bonding.

Next, substrate 310 is removed from the construction shown in FIG. 3Cresulting in the construction shown schematically in FIG. 3D. Substrate310 can be removed using any suitable removing method, such as wet ordry etching methods. For example, an InP substrate 310 can be removed byetching the substrate in, for example, an HCl solution at room or anelevated temperature. As another example, a Ge substrate can be removedby etching the substrate in, for example, a CF₄/O₂ plasma as describedin, for example, R. Venkatasubramanian, et al., “Selective PlasmaEtching of Ge Substrates for Thin Freestanding GaAs—AlGaAsHeterostructures,” Appl. Phys. Lett. Vol. 59, p. 2153 (1991). As anotherexample, a GaAs substrate can be removed by etching the substrate in,for example, a solution of NH₄OH and sufficiently concentrated H₂O₂ atroom or an elevated temperature and, for example, with aggressiveagitation.

Next, second mirror 160 is fabricated on semiconductor multilayer stack130 resulting in the construction shown schematically in FIG. 3E, wherethe details of second mirror 160, some of which are shown in FIG. 1, arenot shown in FIG. 3E for ease of viewing. The different layers in secondmirror 160 can be fabricated on semiconductor multilayer stack 130using, for example, chemical and/or physical vapor deposition methods.

It should be appreciated that the fabrication process described in FIGS.3A-3E is an exemplary process and other methods can be employed tofabricate the constructions disclosed in this application. Furthermore,it should be appreciated that the fabrication steps described in FIGS.3A-3E may include additional steps. For example, the fabrication processmay include one or more intermediate steps in between any two disclosedsequential steps.

In the exemplary light source 100 of FIG. 1, pump light source 170,VCSEL 190, and light management optics 180 are co-linear and centered ona same axis 195 (parallel to the y-axis). The pump light is incident onan input surface, such as input surface 128, of the VCSEL. Convertedlight 178 is emitted, or exits, from an output or exit surface, such asoutput surface 129, of the VCSEL, where output surface 129 is oppositeto and different from input surface 128. In general, differentcomponents or portions of light source 100 can be centered on differentaxes. For example, FIG. 4 is a schematic side-view of a light source 400having a pump light source 470 similar to pump light source 170, a lightmanagement optics 480 similar to light management optics 180, a VCSEL490 similar to VCSEL 190, and a heat sink 405 similar to heat sink 105,where a portion of light source 400 is located on first axis 401 andanother portion of light source 400 is located on second axis 402.

Pump light source 470 and light management optics 480 are centered onaxis 401. Pump light source 470 emits light 472 at the first wavelengthλ₁ that is generally centered on and propagates along axis 401. Lightmanagement optics 480 focus light 472 as light 474 generally centered onand propagating along axis 401.

VCSEL 490 is centered on second axis 402, where axis 402 makes an angleθ with axis 401. VCSEL 490 converts at least a portion of incident light474 at the first wavelength λ₁ to a converted output light 478 at thelonger wavelength λ₂ that is generally centered on and propagates alongaxis 402.

VCSEL 490 is disposed on a heat sink 405 similar to heat sink 105 andincludes a first mirror 420, a semiconductor multilayer stack 430similar to semiconductor multilayer stack 130, and a second mirror 460similar to second mirror 160.

Incident or pump light 474 enters the VCSEL from an input surface 429 ofthe VCSEL and converted, re-emitted, or exit light 478 exits VCSEL fromthe same surface. In the exemplary light source 400, the input surfaceof the VCSEL is the same as the output surface of the VCSEL. In theexemplary light source 400, first mirror 420 need not be opticallytransmissive to incident light 474 since incident light 474 is primarilyreflected, and not transmitted, by first mirror 420. First mirror 420includes a reflective multilayer stack 415, similar to first mirror 120,disposed on an optional highly reflective metal layer 410. In somecases, reflective metal layer 410 can be optically opaque at the firstwavelength λ₁.

In some cases, optional metal reflector 410 can increase thereflectivity of first mirror 420. In some cases, metal reflector 410 caninclude, for example, Al, Ag, Au, or any combination thereof. In somecases, the optical reflectance of metal reflector 410 at the secondwavelength λ₂ is at least 50%, or at least 60%, or at least 70%, or atleast 80%, or at least 90%.

In some cases, metal reflector 410 layer can reduce the number oflayers, such as dielectric layers, that are needed to achieve a desiredoverall reflectivity for mirror 420. In such cases, the thermalconductance between semiconductor multilayer stack 430 and heat sink 405can be improved because of the reduced separation between the twocomponents. In some cases, a portion of the incident light at the firstwavelength that is reflected by first mirror 420, can be reflected backby semiconductor multilayer stack 430 as light 475. In such cases, metalreflector 410 can recycle light 475 by reflecting at least a portion ofthe light back towards the semiconductor multilayer stack so that thelight can be absorbed by the semiconductor multilayer stack, therebyincreasing the overall conversion efficiency of the VCSEL.

Semiconductor multilayer stack 430 absorbs at least a portion of light474 at the first wavelength and re-emits at least a portion of theabsorbed light as light 476 at the second wavelength λ₂, where light 476is generally centered on and propagates along axis 402. Converted light476 is, at least partially, transmitted by second mirror 460 as outputlight 478. In some cases, output light 478 of light source 400 caninclude lights at both the first and second wavelengths. In some cases,the absorption of semiconductor multilayer stack 430 and/or thereflectance of second mirror 460 at the first wavelength can besufficiently high so that output light 478 has no or very little lightat the first wavelength.

In the exemplary light source 100 of FIG. 1, VCSEL 190 includesrespective first and second end mirrors 120 and 160 directly disposed onopposite sides of semiconductor multilayer stack 130 where the two endmirrors form an optical cavity for light at the second wavelength λ₂. Insome cases, an end mirror in a VCSEL can be separated or spaced apartfrom the semiconductor multilayer stack as shown in FIG. 5.

FIG. 5 is a schematic side-view of a light source 500 that includes pumplight source 170 emitting light 172 at the first wavelength λ₁, heatsink 105, and a VCSEL 590 that includes first end mirror 120,semiconductor multilayer stack 130 disposed on the first end mirror, anoptional turning mirror 550, and a second end mirror 560, where the twoend mirrors form an optical cavity for light at λ₂. In some cases,turning mirror 550 can be a dichroic turning mirror. Second end mirror560 is separated or spaced apart from semiconductor multilayer stack 130by a gap 505. In some cases, gap 505 between end mirrors 120 and 560 caninclude an air gap. An advantage of light source 500 is that one or moreadditional optional optical components, such as turning mirror 550, canbe included inside the optical cavity. Other exemplary optional opticalcomponents include optical filters, polarizers, lenses, dichroicmirrors, and the like.

Semiconductor multilayer stack 130 absorbs at least a portion of light172 and re-emits at least a portion of the absorbed light as light 576at the second wavelength λ₂. Light 576 at the second wavelength isredirected by dichroic turning mirror 550 towards second end mirror 560.Second end mirror 560 is, at least functionally, similar to secondmirror 160 and is partially transmissive and partially reflective at thesecond wavelength λ₂. A portion of light at the second wavelength istransmitted by the second end mirror as output light 520 emitted bylight source 500.

In some cases, semiconductor multilayer stack 130 includes a quantumwell that includes a Cd(Mg)ZnSe alloy. In some cases, second end mirror560 can have an additional optical function, such as an optical powerfor, for example, focusing light 576 or 520.

FIG. 6 is a schematic side-view of a light emitting system 600 thatincludes an optical cavity 690 that is similar to VCSEL 190 and isbonded to an electroluminescent device 670 that is similar to pump lightsource 170. In some cases, electroluminescent device 670 can be acoherent laser diode (LD) or an incoherent light emitting diode (LED).Electroluminescent device 670 emits light 672 at the first wavelengthλ₁. Optical cavity 690 includes first mirror 120, semiconductormultilayer stack 130, and second mirror 160. Semiconductor multilayerstack 130 receives at least a portion of light 672 at the firstwavelength, and converts at least a portion of the received light 674 atthe second wavelength λ₂. At least a portion of re-emitted or convertedlight to light 674 is transmitted by second mirror 160 as output light678.

In some cases, light 678 that exits light emitting system 600 issubstantially monochromatic, meaning that the exiting light issubstantially light at the second wavelength λ₂ and includes little orno first wavelength light at λ₁. In such cases, the integrated or totalemission intensity of all light at the second wavelength λ₂ that exitlight emitting system 600 is at least 4 times, or at least 10 time, orat least 20 times, or at least 50 times, the integrated or totalemission intensity of all light at the first wavelength λ₁ that exitlight emitting system 600. Integrated emission intensity of lightemitting system 600 can be determined by integrating the outputintensity of the system at one or more wavelengths over all emissionangles and directions which, in some cases, can be 4π square radians or4π steradians.

In some cases, a portion of any unconverted light at the firstwavelength λ₁ may exit light emitting system 600 and become part of theoutput light. In such cases, output light 678 can include light at bothwavelengths λ₁ and λ₂. In such cases, light exiting light emittingsystem 600 along different directions can have different spectral, suchas color, properties. For example, light traveling along differentdirections can have different proportions of the first and secondwavelengths light. For example, output light 678 can propagatesubstantially along a first direction 630 (y-axis) and output light 679can propagate substantially along a second direction 640. In some cases,lights 678 and 679 can have different spectral properties. For example,light 678 can have a larger second wavelength content than light 679. Insome cases, optical cavity 690 enhances emission of light from an activetop surface 650 of the light emitting system and suppresses emission oflight from one or more sides of the light emitting system, such as sides652 and 654 of the optical cavity. In such cases, output lights 678 and679 can have substantially the same spectral characteristics. Forexample, in such cases, light 678 can have a first color C₁ with CIEcolor coordinates u₁′ and v₁′ and color coordinates x₁ and y₁ and light679 can have a second color C₂ with color coordinates u₂′ and v₂′ andcolor coordinates x₂ and y₂, where colors C₁ and C₂ are substantiallythe same. In such cases, the absolute value of each of the differencesbetween u₁′ and u₂′ and between v₁′ and v₂′ is no more than 0.01, or nomore than 0.005, or no more than 0.004, or no more than 0.003, or nomore than 0.002, or no more than 0.001, or no more than 0.0005; and thedifference Δ(u′,v′) between colors C₁ and C₂ is no more than 0.01, or nomore than 0.005, or no more than 0.004, or no more than 0.003, or nomore than 0.002, or no more than 0.001, or no more than 0.0005. In somecases, the angle α between directions 630 and 640 is not less than about10 degrees, or not less than about 15 degrees, or not less than about 20degrees, or not less than about 25 degrees, or not less than about 30degrees, or not less than about 35 degrees, or not less than about 40degrees, or not less than about 45 degrees, or not less than about 50degrees, or not less than about 55 degrees, or not less than about 60degrees, or not less than about 65 degrees, or not less than about 70degrees.

As used herein, an active top surface 650 means that portion of the topsurface of the light emitting system through which light is emitted.Active top surface 650 has a minimum lateral dimension W_(min). In somecases, W_(min) can be in a range from about 50 μm to about 1000 μm, orfrom about 100 μm to about 600 μm, or from about 200 μm to about 500 μm.In some cases, W_(min) can be about 250 μm, or about 300 μm, or about350 μm, or about 4000 μm, or about 4500 μm. In some cases, the minimumwidth W_(min) can be in a range from about 1 μm to about 50 μm, or fromabout 1 μm to about 40 μm, or from about 1 μm to about 30 μm.

The sides, such as sides 652 and 654, of optical cavity 690 define anexit aperture having a maximum height T_(max), where, in some cases,T_(max) can be the maximum edge thickness of the optical cavity. Thesides, including for example sides 652 and 654, of the optical cavitydefine a largest exit or clear aperture having a maximum height T_(max)through which light at the first wavelength λ₁ can exit the opticalcavity. In general, T_(max) corresponds to the sum of the thicknesses ofthe various layers in the optical cavity that are at least substantiallyoptically transparent at λ₁. In some cases, T_(max) corresponds to thesum of the thicknesses of all of the semiconductor layers in the opticalcavity. In some cases, T_(max) corresponds to the maximum edge thicknessof the optical cavity excluding the edge portions that are nottransparent at λ₁. In some cases, T_(max) is in a range from about 1 μmto about 1000 μm, or from about 2 μm to about 500 μm, or from about 3 μmto about 400 μm. In some cases, T_(max) is about 4 μm, or about 10 μm,or about 20 μm, or about 50 μm, or about 100 μm, or about 200 μm, orabout 300 μm.

In some cases, the ratio W_(min)/T_(max) is large enough so that opticalcavity 690 enhances emission of light from active top surface 650 oflight emitting system 600 and suppresses emission of light from sides652 and 654 of the optical cavity. For example, in such cases, the ratioW_(min)/T_(max) is at least about 30, or at least about 40, or at leastabout 50, or at least about 70, or at least about 100, or at least about200, or at least about 500.

In some cases, emission through sides of optical cavity 690 can besuppressed by placing a light blocking construction 610 along side 652and a light blocking construction 612 along side 654. Light blockingconstructions 610 and 612 can block light that propagates side ways inthe optical cavity by any means that may be desirable and/or availablein an application. For example, in some cases, light blockingconstructions 610 and 612 can block the light primarily by absorbing thelight. In some other cases, light blocking constructions 610 and 612 canblock the light primarily by reflecting the light. In some cases, theconstructions block the light partly by absorption and partly byreflection.

In some cases, emission through sides of the light emitting system, suchas sides 622 and 626 of electroluminescent device 670, can be furthersuppressed by placing a light blocking construction 620 along side 622of electroluminescent device 670 and a light blocking construction 624along side 626 of the electroluminescent device. In such cases, asubstantial portion of the first wavelength light that exitselectroluminescent device 670 and is received by optical cavity 690,exits the electroluminescent device through an active top surface 629 ofthe electroluminescent device. For example, in such cases, at least 50%,or at least 60%, or at least 70%, or at least 80%, or at least 90%, orat least 95%, or at least 98% of first wavelength light 672 that exitselectroluminescent device 670 and is received by optical cavity 690,exits the electroluminescent device through active top surface 629 ofthe electroluminescent device.

Sides 622 and 626 of electroluminescent device 670 define an exitaperture having a maximum height T1 _(max), where, in some cases, T1_(max) can be the maximum edge thickness of the electroluminescentdevice. The sides, including for example sides 622 and 626, of theelectroluminescent device define a largest exit or clear aperture havinga maximum height T_(max) through which light at the first wavelength λ₁can exit the electroluminescent device. In general, T_(max) correspondsto the sum of the thicknesses of the various layers in theelectroluminescent device that are at least substantially opticallytransparent at λ₁. In some cases, T_(max) corresponds to the sum of thethicknesses of all of the semiconductor layers in the electroluminescentdevice. In some cases, T_(max) corresponds to the maximum edge thicknessof the electroluminescent device excluding the edge portions that arenot transparent at λ₁. In some cases, T1 _(max) is in a range from about1 μm to about 1000 μm, or from about 2 μm to about 500 μm, or from about3 μm to about 400 μm. In some cases, T1 _(max) is about 4 μm, or about10 μm, or about 20 μm, or about 50 μm, or about 100 μm, or about 200 μm,or about 300 μm.

Active top surface 629 has a minimum lateral dimension W1 _(min). Insome cases, W1 _(min) can be in a range from about 50 μm to about 1000μm, or from about 100 μm to about 600 μm, or from about 200 μm to about500 μm. In some cases, W1 _(min) can be about 250 μm, or about 300 μm,or about 350 μm, or about 4000 μm, or about 4500 μm. In some cases, theminimum width W1 _(min) can be in a range from about 1 μm to about 50μm, or from about 1 μm to about 40 μm, or from about 1 μm to about 30

In some cases, the ratio W1 _(min)/T1 _(max) is large enough so thatelectroluminescent device 670 enhances emission of light from active topsurface 650 of light emitting system 600 and suppresses emission oflight from the sides of the light emitting system, such as sides 622 and626 of the electroluminescent device. For example, in such cases, theratio W1 _(min)/T1 _(max) is at least about 30, or at least about 40, orat least about 50, or at least about 70, or at least about 100, or atleast about 200, or at least about 500.

Other exemplary methods for enhancing emission of light from active topsurface 650 of light emitting system 600 and suppressing emission oflight from the sides of the light emitting system are described in U.S.Patent Application Ser. No. 61/094,180, filed Sep. 4, 2008, which isincorporated herein in its entirety by reference.

FIG. 7 is a schematic light pointer 700 that includes a housing 730 thathouses a battery 710 for energizing a light source 720 via an electricalconnection 715. Once energized, light source 720 emits output light 740that can point to a desired location or designate a desired spot. Lightsource 720 can be any disclosed light source, such as light source 100or 400. In some cases, light source 720 can be a laser diode. In suchcases, light pointer 700 can be a laser pointer 700.

In some cases, light pointer 700 can be handheld, meaning that it can beheld in a user's hand with relative ease and convenience. In such cases,the user can energize light pointer 700 by, for example, operating, suchas pressing, a button 750. In some cases, light pointer 700 can bepen-like, meaning that it can, for example, look like a writinginstrument, such as a pen or pencil.

As used herein, terms such as “vertical”, “horizontal”, “above”,“below”, “left”, “right”, “upper” and “lower”, “top” and “bottom” andother similar terms, refer to relative positions as shown in thefigures. In general, a physical embodiment can have a differentorientation, and in that case, the terms are intended to refer torelative positions modified to the actual orientation of the device. Forexample, even if the construction in FIG. 1 is flipped vertically ascompared to the orientation in the figure, second mirror 160 is stillconsidered to be a top end mirror and first mirror 120 is stillconsidered to be a bottom end mirror.

While specific examples of the invention are described in detail aboveto facilitate explanation of various aspects of the invention, it shouldbe understood that the intention is not to limit the invention to thespecifics of the examples. Rather, the intention is to cover allmodifications, embodiments, and alternatives falling within the spiritand scope of the invention as defined by the appended claims.

1. A light emitting system, comprising: an electroluminescent deviceemitting light at a first wavelength; and an optical cavity enhancingemission of light from a top surface of the light emitting system andsuppressing emission of light from one or more sides of the lightemitting system, the optical cavity comprising a semiconductormultilayer stack receiving the emitted first wavelength light andconverting at least a portion of the received light to light of a secondwavelength, the semiconductor multilayer stack comprising a II-VIpotential well; wherein an integrated emission intensity of all light atthe second wavelength exiting the light emitting system is at least 10times an integrated emission intensity of all light at the firstwavelength exiting the light emitting system.
 2. The light emittingsystem of claim 1, wherein the II-VI potential well comprises Cd(Mg)ZnSeor ZnSeTe.
 3. The light emitting system of claim 1, wherein theelectroluminescent device is so designed that a substantial portion ofthe first wavelength light that is received by the semiconductormultilayer stack, exits the electroluminescent device through a topsurface of the electroluminescent device.
 4. The light emitting systemof claim 1, wherein light emitted by the light emitting system along afirst direction has a first set of color coordinates, and light emittedby the light emitting system along a second direction different than thefirst direction has a second set of color coordinates, the second set ofcolor coordinates being substantially the same as the first set of colorcoordinates.
 5. The light emitting system of claim 4, wherein the firstset of color coordinates are u₁′ and v₁′ and the second set of colorcoordinates are u₂′ and v₂′, and wherein an absolute value of each ofdifferences between u₁′ and u₂′ and between v₁′ and v₂′ is no more than0.003.
 6. The light emitting system of claim 1, wherein the integratedemission intensity of all light at the second wavelength exiting thelight emitting system is at least 50 times the integrated emissionintensity of all light at the first wavelength exiting the lightemitting system.
 7. The light emitting system of claim 1, wherein theelectroluminescent device comprises an LED emitting incoherent light. 8.The light emitting system of claim 1, wherein the electroluminescentdevice comprises a laser diode emitting at least partially coherentlight.
 9. The light emitting system of claim 1, wherein: a primaryportion of the re-emitted second wavelength light exits the lightemitting system from a top surface of the light emitting system having aminimum lateral dimension W_(min), and a substantial fraction of theremaining portion of the re-emitted second wavelength light exits thelight emitting system from one or more sides of the optical cavityhaving a maximum edge thickness T_(max), the ratio W_(min)/T_(max) beingat least about 30; and wherein: a primary portion of the emitted firstwavelength light exits the electroluminescent device from a top surfaceof the electroluminescent device having a minimum lateral dimension W1_(min), and the remaining portion of the emitted first wavelength lightexits the electroluminescent device from one or more sides of theelectroluminescent device having a maximum edge thickness T1 _(max), theratio W1 _(min)/T1 _(max) being at least about
 30. 10. The lightemitting system of claim 9, wherein each of the ratios W_(min)/T_(max)and W1 _(min)/T1 _(max) is at least about
 100. 11. A light pointercomprising the light source of claim
 1. 12. The light pointer of claim11 being a laser pointer.
 13. The light pointer of claim 11 being ahandheld light pointer.
 14. The light pointer of claim 11 furthercomprising a battery for operating the light pointer.